Gui-Feng Yu

Twisted microropes for stretchable devices based on electrospun conducting polymer fibers doped with ionic liquid

We report an effective method to fabricate poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)–polyvinyl pyrrolidone (PEDOT:PSS–PVP) fiber arrays doped with ionic liquid (IL). The twisted microropes were obtained by twisting the electrospun aligned polymer fiber arrays. It was found that the twisted rope exhibited higher electrical conductivity (∼1.8 × 10−4 S cm−1) after IL doping (1.96 wt%) than those without doping (∼0.8 × 10−5 S cm−1), and its conductivity was linearly correlated with strain up to 35% (which is one magnitude larger than previous reports) and showed repeatable cycle loops of tensile-resilience. The extensible rate could reach up to more than 90%, considerably higher than that of ropes without IL doping (∼17%). The results indicate that the twisted PEDOT:PSS–PVP ropes may be used as elastic semiconductors and stretchable sensors.

Electrospun anatase TiO2 nanorods for flexible optoelectronic devices

Titanium dioxide (TiO2) nanorods with anatase phase were successfully fabricated by electrospinning and followed calcination. The TiO2 nanorods were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and UV-visible spectroscopy. The diameter of the TiO2 nanorods was about 60–150 nm and the length was 200 nm–2 μm. Electrical properties under bending were investigated by fixing the device to a curved surface with different curvatures, and the device showed a fast and stable resistance response to curvature changing. Photoelectric properties were studied by irradiation with different light intensities. The device exhibited a short response time (∼10 s) and a high sensitivity (∼103) which increased with the light intensity increasing. These results indicate that electrospun anatase TiO2 nanorods have potential applications in flexible photodetectors and solar cells.

Solvent-free electrospinning of UV curable polymer microfibers

The conventional solution electrospinning (e-spinning) process is facing the trouble of solvent recovery, especially for the industrial mass production of electrospun (e-spun) ultrathin fibers. This study provides a possible strategy, solvent-free e-spinning to solve this problem. By using a modified homemade e-spinning device and UV curable materials as the precursor liquid, all the spinning solution was successfully e-spun into ultrathin fibers without solvent evaporation (weight loss) in an atmosphere of nitrogen and under UV light radiation. The solidification mechanism of the fibers is ascribed to the quick curing of the acrylate bonds in the spinning stream under UV light radiation and without oxygen inhibition in the atmosphere of nitrogen. Such a break-through leads to fabrication of ultrathin fibers by solvent-free e-spinning without solution loss, and provides an eco-friendly approach to prepare new and functional (composite) ultrathin fibers by using a variety of UV curable materials and functional additions.

Ecofriendly fabrication of ultrathin colorful fibers via UV-assisted solventless electrospinning

A new technique to fabricate ultrathin colorful fibers has been developed via ultraviolet (UV)-assisted solventless electrospinning. The precursor solution contains UV curable polyurethane acrylate (PUA) and colorful UV gel nail polish, and can be electrospun into ultrathin fibers without solvent evaporation in the atmosphere of nitrogen, owing to rapid curing of the acrylate bonds in the spinning jet under the radiation of UV light. The resulting fibers have good color fastness and high stretchability (more than 140%). In addition, various fiber colors can be conveniently adjusted and obtained through formulating the recipe of the precursor solution. Compared to the traditional dyeing process, this method is ecofriendly and promising to prepare colorful fibers, which may be used in textiles, clothing, and anticorrosive coatings.

Flexible Polyaniline/Poly(methyl methacrylate) Composite Fibers via Electrospinning and In Situ Polymerization for Ammonia Gas Sensing and Strain Sensing

Conducting polyaniline (PANI) was in situ polymerized at the surface of electrospun poly(methyl methacrylate) (PMMA) fibers to obtain flexible composite fibers. The electrical conductivity of an individual PANI/PMMA composite fiber was estimated to be 2.0 × 10−1 S cm−1 at room temperature. The ammonia sensing properties of the samples were tested by impedance analysis. The PANI/PMMA fibers could obviously respond to low concentration of ammonia at ppb level and could respond to relatively high concentration of ammonia at 10 ppm level quickly. In addition, the sensitivity exhibited a good linear relationship to the ammonia concentration. Particularly, the flexible PANI/PMMA fibers showed a reversible change in electrical resistance with repeated cycles of bending and relaxing, and the electrical resistance decreased with the increase of curvature. These results indicate that the flexible PANI/PMMA composite fibers may be used in toxic ammonia gas detection, strain sensing, and flexible electronic devices.

Electrical conduction mechanism of an individual polypyrrole nanowire at low temperatures

Conducting polypyrrole (PPY) nanowires doped with p-toluene sulfonamide (PTSA) were synthesized by a template-free self-assembly method. Electrical transport characteristics, i.e. current-voltage (I-V) behavior, of an individual PPY/PTSA nanowire have been explored in a wide temperature range from 300 down to 40 K. The fitting results of I-V curves indicated that the electrical conduction mechanism can be explained by the space-charge-limited current (SCLC) theory from 300 down to 100 K. In this temperature range, traps play an important role for this non-crystalline system. The corresponding trap energy and trap concentration have also been calculated based on the SCLC theory. Interestingly, there is no trap at 160 K, different from other temperatures. The obtained carrier mobility for the polymer nanowires is 0.964 cm(2) V(-1) s(-1) on the basis of trap free SCLC theory. In the temperature range of 80-40 K, little current can flow through the nanowire especially at lower voltages, however, the current follows the equation I ∞ (V/Vt-1)(ζ) at higher bias, which could be attributed to Coulomb blockade effect. Additionally, the differential conductance dI/dV curves also show some clear Coulomb oscillations.